The invention relates to a latch needle, in, particular for knitting machines.
Latch needles are used for different types of knitting machines. A latch needle is known, for example, from German Printed Patent Specification 1113537. This latch needle has a needle body with a hook formed onto the end. A latch is positioned pivoting inside a latch slot formed near the hook. With its free end, the so-called latch spoon, the latch can rest on the hook tip and thus close off the trapping clearance. From this closed position, the latch can pivot back to the upright position, in which the trapping clearance is freed. The pivoting movement should be as easy as possible. Modern knitting machines frequently require needles that move easily. Hard to move needles knit unevenly and thus produce a poor loop picture.
The latches of some machines must fall back into the upright position as a result of their own weight. If this does not happen reliably, the danger exists that the latches come in contact with parts of the machine, e.g. the yarn-feed apron, and are bent as a result.
The easy movement of the latch can be achieved by increasing the latch play. However, increasing the latch play worsens the latch guidance even if the needle is still new. With a further increase in wear, the latch guidance becomes less and less precise, thus reducing the operational reliability.
Another problem resulting from increased latch play occurs if the latch is positioned with rivets pressed out of the slot cheeks, as disclosed in U.S. Pat. No. 1,991,140. For the positioning, the latch provided with a bearing opening is inserted into the latch slot. Following this, sections of the slot cheeks are pressed or punched toward the inside with the aid of two plunging tools (engravers), such that these cheek portions enter the bearing opening in the latch and form a bearing rivet for the latch. This operation requires relatively little latch play. The latch forms a counter stop for the pressing or punching operation, particularly with the region surrounding the bearing opening. If the latch is noticeably smaller than the latch slot, the slot cheeks are bent toward the inside during the punching operation, thus preventing the latch needle from being produced with the desired quality.
Starting with this premise, it is the object of the invention to provide a latch needle with a latch that is designed to move easily and is precisely guided.
This object is solved with a latch needle having features in accordance with the present invention.
The latch needle according to the invention has a latch comprising a latch spoon and a latch shaft, the side surface or surfaces of which are divided. A first surface area surrounds the bearing opening where it ensures a slight latch play on the side. The following second surface area permits a greater latch play, meaning the distance to the neighboring slot cheek is increased, thus reducing contact with the wall to small surface areas or omitting it completely. As a result, it is possible to produce latch needles with latches that move extremely easily. For this, the surface area surrounding the bearing opening can be designed such that the latch is guided with little play and thus very precisely. On the other hand, the following second surface area can be set back, thus reducing the thickness of the latch shaft by a few 1000th millimeters (for example 0.03 mm). During the opening and closing of the latch, meaning the pivoting movement between closed position and upright position, the second surface area that extends along the latch shaft is thus prevented from being wedged into the slot or from experiencing strong friction inside the slot. The set back surface area contributes only slightly or not at all to the side guidance of the latch. A functional separation between the surface areas exists. The first surface area surrounding the latch opening primarily is responsible for the side guidance of the latch. This can possibly be recognized by the fact that the side play of the latch is respectively the same in the closed position or the upright position and an in an intermediate position. Having little latch play in the area of the rivet ensures a good guidance of the latch inside the slot.
The insignificant latch play inside the slot in the region of the guide surface of the first surface area considerably facilitates the process of pressing out the rivet, meaning the pressing or punching operation during which sections of the cheek wall are pressed into the bearing opening of the latch. The insignificant play prevents the cheek walls from being squeezed together when punching out the rivets and thus deforming the needle. Especially precise needles can be produced as a result.
On the other hand, the increased play between latch shaft and cheek wall reduces the danger of threads being wedged in, damaged or cut between latch and cheek (slot sidewall). In addition, it also reduces the danger that fibers or dirt will enter the slot and result in a jamming of the latch.
Owing to the fact that the latch guidance is essentially assumed by the surface areas surrounding the latch, a noticeably larger spacing can exist between the remaining latch flanks of the latch shaft and the slot cheeks. The difference between the thickness of the latch shaft in the region of the latch hole and in the region of the latch head or latch spoon can amount to several one-hundredth millimeters, without this worsening the latch guidance.
Despite the improvement in the easy movement of the latch, the latch is guided with such precision that the latch makes even better contact with the hook. As a result of the increased precision during the operation of the needle, the wear between latch and hook can be reduced. In addition, the latch shaft does not make frictional contact over its complete length that is submerged in the slot, but only in the bearing region on the slot cheek.
Both side surfaces of the latch shaft for the latch needle are preferably designed identical, so that both side surfaces are divided into separate surface areas. The latch in that case is designed to be symmetrical to a center plane.
A line-shaped or strip-shaped separation or transition area is formed between the two separate surface areas. In other words, the separation area, for example, takes the shape of a line, an edge or a step or forms a slightly curved transition area. The separation area of one preferred embodiment is a step, which results in a large distance between cheek and surface area along the area recessed by the step. The surface area can be planar or can be curved in one or several directions or can be structured. The same is true for the other surface area surrounding the bearing opening, which can also be planar or otherwise formed.